Let the displacement of the particle executing SHM at any instant t is , x=Asinωt
Velocity, v=dtdx=dtdAsinωt=Awcosωt
The mean velocity of the particle averaged over quarter oscillation is (v)0→T/4=0∫T/4dt0∫T/4vdt=T/40∫T/4Aωcosωtdt T/4ωAω[sinωt]0T/4 =T/4A[sinωt]0T/4=T4A